Manufacture of menthol



Patented Apr. 19', 1927.

- UNITED STATES Km scrrormrorr, or nussannoar oanaxassnn' GERMANY, assrenoa r mnnscn'xAmna-rnm GESELLSCHAIT HIT BESCHBANK'IER- HAFTUNG, OI DUSBBLDOB'I-OB 6mm.

muracrunn OF IENTHOI:

Io Drawing. Application fled Iovember 88, 1922, Serial No. 608,853, and in Germany November 28, 1921.

The present invention refers to the manufacture of racemicmenthol being optically inactive, but having besides this'point the properties of the activementhol as obtained from natural sources. Sabatier and Brunel have described (see Comptes rendus, Volume 137, page1268 and volume 140, page 252) that the vapours of thymol when conducted over heated nickel give in the lgresence of hydrogen two isomeric mentho and varying amounts of menthone, Pickard and Littlebury (Chemical Society Journal Volume 101, page 109, Transactions 1921) have cleared up the chemical constitution of the menthols obtained according to Sabatier and Brunel.

According to the theo' two inactive menthones (i-menthone an i-isomenthone) are possible and 4 inactive menthols, corresponding to the 2 inactive menthones.

The present process consists in heating thymol in presence of catalysts promoting the hydrogenation with hydrogen under pressure, separating by physical processes from the reaction product the crystallizable,

crystalline racemate' of menthol and subjecting the remaining liquid, non crystallizable mixture of isomeric menthols to a new hydrogenation, process with catalysts under pressure, if desired after having been added to fresh thymol. By the hydrogenation of thymol with catalysts under pressure a mixture of several substances is formed, the racemate of the natural active menthol (which may be'separated by physical o erations, as fractional distillation or a eezing process, from liquid menthols) and liquid menthols, hereinafter called liquid menthols mixture.-. The liquid menthols mixture consists ofjthe inactive alcohols of the 4 i-menthone (semicarbazone melting at 158 degrees centigrade), called i-menthol, melting point 34 degrees centlgrade' and i-neoof resisting high pressures, for instance an.

autoclave.

The liquid menthols mixture, separated from the racemate'of the natural active menthol may be heated again with catalysts promotmg the hydrogenation and hydrogen under pressure or the said liquid menthols -mi xturg may be added to thymol and the said mixture heated with catalysts promot-- arates the menthol from the liquid menthols mixture either by a freezing process or by fractional distillation. By the freezing process (for instance at zero or minus degrees centigrade) the menthol is solidified whereas the liquid menthols mixture remains fluid and may be decanted or othervilisia separated from the crystallized men t o The liquid menthols mixture thus obtained is heated with 250-500 grams nickel catalyst and h drogen to about 200 degrees centigrade un er a nressure of 5-30 atmospheres. The reaction product is then treated as above. described for the hydrogenation product of thymol.

Instead of mixture with hydrogenation catalysts and hydrogen as described I may add the liquid menthol mixture to thymol, as for instance 25 kilograms,-and heat the said mixture with "hydrogen and 500-750 grams nickel catalyst or more to about 200 degrees centigrade undera pressure of about 5-30 atmostreating the liquid mentholor freezing pheres. The reaction product is then treated as above described for the hydrogenation product of thymol. i p a I claim 1. Theprocess for manufacturing inactive menthol which consists in heating thymol with catalysts promoting the hydrogenation and hydrogen under pressure, separatin' the inactive menthol from the liqud ment 01s mixture by 'physical' methods and heating the letter mixture with catalysts'promoting 3. The process for manufacturing inactive the hydrogenation and hydrogen under menthol which consists in heating thymol pressure. with catalysts promoting the hydrogenation 15 2. The process for manufacturing inactive and hydrogen under pressure, as! rating the 5 menthol which consists in heating thymol inactive menthol from the liquid menthols with'catalysts promoting the hydrogenation mixture by subjecting the mass to a freezand hydrogen under pressure. separating the l g process and heating the liquid menthols inactive menthol from the liquid menthols ml ure wi h c lllV tpromoting the hy- 20 mixture, adding the, latter to a, new portion drogenation and hydrogen under pressure- 10 f th l d h ti thi i t ith In testimpnv whereof I hereunto affix my catalysts promoting the hydrogenation and g l llmhydrogen under pressure. KARL SCHOLLKOPF. 

